1. Field of the Invention
The present invention relates to a camera module mounted on an automotive vehicle for taking images for assisting a driver.
2. Description of Related Art
Various devices for automatically operating on-board systems are known. For example, a device for automatically turning on or off a headlight, a device for automatically operating a windshield wiper and a device for automatically detecting obstacles located in front of a vehicle have been actually used. It is necessary to provide respective sensors for these devices: a luminance sensor for the automatic lighting device, a raindrop sensor for the automatic wiper device and an ultrasonic sensor for obstacle-detecting device. To mount these various sensors on an automotive vehicle, not only a large mounting space is required but also considerably high costs and high power consumption are unavoidable.
On the other hand, various devices for assisting a driver have been proposed. For example, a device for detecting obstacles which are invisible at night, and a device for driving a vehicle at a constant speed within a predetermined driving lane have been proposed. It is necessary to provide reliable information to successfully operate these assisting devices. Image information taken by a camera device that shows many things including obstacles in front of a vehicle and lines defining a driving lane is one of the most valuable information for the assisting devices.
JP-A-2001-147278 exemplifies a device detecting raindrops through an image taken by a camera. A windshield wiper is automatically operated when the raindrops are detected. Generally, much more information is obtained from images taken by a camera device than from specific sensors such as a light sensor, a rain sensor or an ultrasonic sensor. Information obtained from images can be used in place of various pieces of information obtained from specific sensors. In this manner, the number of sensors to be mounted on a vehicle would be reduced, and mounting spaces and power consumption would be saved.
The device proposed by JP-A-2001-147278, however, detects only raindrops on a windshield because a camera used in the device is focused on the surface of the windshield. Obstacles or front vehicles cannot be detected by the camera because these are located at a certain distance from a vehicle. It could be possible to adjust the focal distance of the camera to detect both of close and distant objects. However, a certain time is required to adjust the focal distance in the camera device, which would be detrimental to safe driving.